Research On Breakage Mechanism Of End Mill Based On Thermal-mechanical Coupled Stress Field In High Speed Milling

The tool which was affected by high mechanical stress, thermal stress or thermal shock, etc. in a highly non-linear dynamic thermal-mechanical coupling field of high speed milling process bechanced breakage easily. Tool wear would affect the workpiece processing quality and efficiency seriously. In recent, the study of tool breakage mainly existed the following problems: most of the research was restricted to a single physical field like stress field, temperature field. The established model was a single model of cutting force and temperature. The geometric model which was simplified planar or deviation angle was imprecise for solid modeling of end mill, and loading method of force or temperature was a fixed value or linear loading, and the gap of loading position was far form actual processing. The object of study was reasonable shape tool, such as turning tool and milling insert. In this paper, the object of study was solid carbide coated inner-cooled end mill of high speed milling. Dynamic milling numerical model of end mill under thermal-mechanical coupling in high speed milling was established based on the experimental data, dynamics, finite element and tool-chip friction theory. Breakage mechanism of end mill was discussed through the analysis of experimental data and simulation results under thermal-mechanical coupling.Firstly, tool-chip friction theory of study of tribological behavior was emphatically analyzed under high speed condition. Physics equations of friction system between tool and chip which was divided into adhesive and sliding friction was proposed. The two-dimensional mathematical model of unequal cutting thickness was established based on the finite element simulation method in high speed milling. In simulation results, chip morphology of small bending verified the feasibility of bond-slip model, cutting stress field distributed unevenly in the process of cutting,the maximum stress occurred in the deformation zone. The maximum temperature of the cutting tool occurred near the tip and the cutting edge in the processing of cutting.Secondly, dynamic model of thermal-mechanical coupling numerical for end mill was established in high-speed milling. The dynamic simulation model close to actural was established based on the geometry models of internal cooling end mill and workpiece which was built by reverse engineering and the average coefficient of friction which was obtained by orthogonal experiment method. And the milling force, temperature changing field and chip morphology of simulation were analyzed, the fact was revealed that most of cutting heat was taken away by the chips in high-speed milling process. The simulation results were compared with experimental data which proved the correctness of the model.Single factor and orthogonal experiments of high speed milling were implemented. The influences of milling parameters on milling force and temperature were analyzed by using mathematical statistical methods(analysis of variance and range). The mutual influence between force and temperature was also analyzed by a image drawn with Matlab. The results showed that factors of milling force and milling temperature were consistent and the greatest impact parameter was milling depth.Finally, breakage morphology of the mill was observed by scanning electron microscopy(S-3400N-II and S-4800) and breakage mechanism was analyzed. The reliability of the model was verified by comparing the damage location with the maximum temperature position(tool tip, the main cutting edge, rake, flank) of mill in the simulation.